The present invention relates to a process for preparing an ethylene polymer composition, particles of ethylene polymer composition and a film obtained from the particles of ethylene polymer composition. More particularly, the invention relates to a process for preparing an ethylene polymer composition of excellent particle morphology, which comprises polymerizing ethylene with high activity through two-step polymerization using a specific catalyst, particles of ethylene polymer composition which have excellent particle morphology, scarcely suffer sintering and are capable of efficiently undergoing subsequent processes, and a film obtained from the particles of ethylene polymer composition and having small gauge-variation and excellent tear strength.
Ethylene polymers, such as homopolyethylene, a linear low-density ethylene polymer (LLDPE) and an ethylene xcex1-olefin copolymer, are excellent in transparency, mechanical strength, etc., and hence they have been widely used for films and the like.
For preparing such ethylene polymers, various processes have been heretofore known, and it is known that the ethylene polymers can be prepared with high polymerization activity by the use of, as a polymerization catalyst, a Ziegler catalyst containing a titanium catalyst component composed of titanium, magnesium, a halogen, and optionally, an electron donor. It is also known that especially when a solid titanium catalyst component obtained from a halogen-containing magnesium compound that is prepared as a liquid compound, a liquid titanium compound and an electron donor is used as the titanium catalyst component, the ethylene polymers can be prepared with high activity.
By the way, if it becomes possible to polymerize ethylene and an xcex1-olefin with much higher activity in the preparation of the ethylene polymers, not only the productivity is enhanced, but also the amount of a catalyst residue based on the polymer, particularly the amount of halogen, is decreased, and hence problems, such as mold rusting in the molding process, can be solved. On this account, a process for preparing an ethylene polymer, in which ethylene and an xcex1-olefin can be polymerized with much higher activity, has been desired.
As a process for polymerizing ethylene with high activity, there has been recently proposed, for example, a process wherein an ethylene polymerization catalyst containing a solid titanium catalyst component obtained by contacting a liquid magnesium compound, a liquid titanium compound and an organosilicon compound having no active hydrogen (Japanese Patent Laid-Open Publication No. 328514/1997) or a process wherein an olefin polymerization catalyst containing an aluminum compound selected from a reaction product of aluminosiloxane, aluminum alkyl and calixarene and a reaction product of aluminum alkyl and cyclodextrin, a halogen-containing magnesium compound and a titanium compound (Japanese Patent Laid-Open Publication No. 53612/1998), and preparation of polymers of excellent particle morphology using these catalysts has been proposed.
Under such circumstances, establishment of a process for more efficiently preparing an ethylene polymer industrially has been strongly desired. Immediately after the polymerization, an ethylene polymer is usually obtained in the form of a powder irrespective of the polymerization type such as slurry polymerization or gas phase polymerization, and it is desirable to prepare an ethylene polymer having excellent fluidity, containing no finely powdered particles and having excellent particle morphology, namely, an ethylene polymer having a narrow particle size distribution. The ethylene polymer having excellent particle morphology has various advantages such as an advantage that it can be used as it is without pelletization, depending upon the purpose. In addition, development of an ethylene polymer scarcely having tackiness at high temperatures, that is, scarcely suffering sintering, has been strongly desired.
The present invention has been made under such circumstances as described above, and it is an object of the invention to provide a process for preparing an ethylene polymer composition in which ethylene and an xcex1-olefin can be polymerized with high activity and an ethylene polymer composition having excellent particle morphology, scarcely suffering sintering and having excellent moldability can be efficiently prepared. It is another object of the invention to provide particles of ethylene polymer composition which have excellent moldability, scarcely suffer sintering and have a small particle size distribution and to provide a film obtained from the particles of ethylene polymer composition and having small gauge-variation and excellent tear strength.
The process for preparing an ethylene polymer composition according to the invention is a process comprising:
(I) a step of polymerizing ethylene or ethylene and another xcex1-olefin to prepare an ethylene polymer (i) having an xcex1-olefin content of not more than 30% by weight and an intrinsic viscosity [xcex7] of at least 1.5 times the intrinsic viscosity of the following ethylene polymer (ii) and ranging from 1 to 12 dl/g, and
(II) a step of polymerizing ethylene or ethylene and another xcex1-olefin to prepare an ethylene polymer (ii) having an xcex1-olefin content of not more than 15% by weight and an intrinsic viscosity [xcex7] of 0.3 to 3 dl/g,
said steps (I) and (II) using an ethylene polymerization catalyst containing a solid titanium catalyst component obtained by contacting (a) a liquid magnesium compound with (b) a liquid titanium compound in the presence of (c) an organosilicon compound or an organosilicon aluminum compound,
wherein the step (II) is carried out in the presence of the ethylene polymer (i) obtained in the step (I) or the step (I) is carried out in the presence of the ethylene polymer (ii) obtained in the step (II), to prepare an ethylene polymer composition having an intrinsic viscosity [xcex7] of 1 to 6 dl/g and a density of not less than 0.94 g/cm3.
In the process for preparing an ethylene polymer composition according to the invention, the step (I) and the step (II) are preferably carried out by slurry polymerization.
The particles of ethylene polymer composition according to the invention are prepared by the above process, comprise an ethylene polymer composition having a melt flow rate, as measured at 190xc2x0 C. in accordance with ASTM D 1238E, of 0.0001 to 0.5 g/10 min and a molecular weight distribution (Mw/Mn) of 20 to 45, and have:
a particle size distribution index, as determined by the following formula, of 1.1 to 2.0,
Particle size distribution index={square root over (Polymer D84/Polymer D16)}
wherein Polymer D16 is a particle diameter obtained when 16% by weight of the whole particles of ethylene polymer composition can be sieved, and Polymer D84 is a particle diameter obtained when 84% by weight of the whole particles of ethylene polymer composition can be sieved,
a bulk density of 0.30 to 0.45 g/ml, and
a fluidity index of 45 to 90.
When the particles of ethylene polymer composition obtained by the invention are applied to film use, the resulting film has small gauge-variation and excellent tear strength.
The film according to the invention is obtained from the particles of ethylene polymer composition and has small gauge-variation and excellent tear strength.
The process for preparing an ethylene polymer composition, the particles of ethylene polymer composition and the film obtained from the particles of ethylene polymer composition according to the invention are described in detail hereinafter.
The meaning of the term xe2x80x9cpolymerizationxe2x80x9d used herein is not limited to xe2x80x9chomopolymerizationxe2x80x9d but may comprehend xe2x80x9ccopolymerizationxe2x80x9d. Also the meaning of the term xe2x80x9cpolymerxe2x80x9d used herein is not limited to xe2x80x9chomopolymerxe2x80x9d but may comprehend xe2x80x9ccopolymerxe2x80x9d.
In the process for preparing an ethylene polymer composition according to the invention, an ethylene polymerization catalyst containing a specific solid titanium catalyst component is employed.
The ethylene polymerization catalyst for use in the invention contains a solid titanium catalyst component obtained by contacting (a) a liquid magnesium compound with (b) a liquid titanium compound in the presence of (c) an organosilicon compound or an organosilicon aluminum compound.
The ingredients used for preparing the solid titanium catalyst component are described below.
(a) Liquid Magnesium Compound
The magnesium compound used for preparing the solid titanium catalyst component for use in the invention is a liquid magnesium compound, and when the magnesium compound is solid, it is changed to liquid prior to use. As the magnesium compound, a magnesium compound having reducing ability (a-1) or a magnesium compound having no reducing ability (a-2) is employable.
(a-1) Magnesium Compound Having Reducing Ability
The magnesium compound having reducing ability is, for example, an organomagnesium compound represented by the following formula:
XnMgR2xe2x88x92n
wherein n is a number of 0xe2x89xa6n less than 2, R is hydrogen, an alkyl as group of 1 to 20 carbon atoms, an aryl group of 6 to 20 carbon atoms or a cycloalkyl group or 3 to 20 carbon atoms, when n is 0, two of R may the same or different, and X is a halogen.
Examples of the organomagnesium compounds having reducing ability include dialkylmagnesium compounds, such as dimethylmagnesium, diethylmagnesium, dipropylmagnesium, dibutylmagnesium, diamylmagnesium, dihexylmagnesium, didecylmagnesium, octylbutylmagnesium and ethylbutylmagnesium; alkylmagnesium halides, such as ethylmagnesium chloride, propylmagnesium chloride, butylmagnesium chloride, hexylmagnesium chloride and amylmagnesium chloride; alkylmagnesium alkoxides, such as butylethoxymagnesium, ethylbutoxymagnesium and octylbutoxymagnesium; and butylmagnesium hydride.
(a-2) Magnesium Compound Having no Reducing Ability
Examples of the magnesium compounds having no reducing ability include:
magnesium halides, such as magnesium chloride, magnesium bromide, magnesium iodide and magnesium fluoride;
alkoxymagnesium halides, such as methoxymagnesium chloride, ethoxymagnesium chloride, isopropoxymagnesium chloride, butoxymagnesium chloride and octoxymagnesium chloride;
aryloxymagnesium halides, such as phenoxymagnesium chloride and methylphenoxymagnesium chloride;
alkoxymagnesiums, such as ethoxymagnesium, isopropoxymagnesium, butoxymagnesium, n-octoxymagnesium and 2-ethylhexoxymagnesium;
aryloxymagnesiums, such as phenoxymagnesium and dimethylphenoxymagnesium;
carboxylic acid salts of magnesium, such as magnesium laurate and magnesium stearate;
magnesium metal; and
magnesium hydrate.
The magnesium compound having no reducing ability (a-2) may be a compound derived from the magnesium compound having reducing ability (a-1) or a compound derived during the preparation of the catalyst component. In order to derive the magnesium compound having no reducing ability (a-2) from the magnesium compound having reducing ability (a-1), the magnesium compound having reducing ability (a-1) has only to be contacted with, for example, a compound having an OH group or a reactive carbon-oxygen bond, such as an alcohol, a ketone, an ester, an ether or a siloxane compound, or a halogen-containing compound, such as a halogen-containing silane compound, a halogen-containing aluminum compound or an acid halide.
In the present invention, the magnesium compound having no reducing ability (a-2) can be derived from the magnesium compound having reducing ability (a-1) using the later-described organosilicon compound or organosilicon aluminum compound (c). In this case, the magnesium compounds can be used in combination of two or more kinds.
The magnesium compound may be a complex salt or a double salt with a compound of a metal other than magnesium, such as aluminum, zinc, boron, beryllium, sodium or potassium, e.g., the later-described organoaluminum compound, or can be used as a mixture with the compound of the above metal.
As the liquid magnesium compound used for preparing the solid titanium catalyst component, a magnesium compound other than those described above is also employable. In the resulting solid titanium catalyst component, however, the magnesium compound is preferably present in the form of a halogen-containing magnesium compound. Therefore, if a magnesium compound containing no halogen is used, it is preferable to contact the magnesium compound with a halogen-containing compound during the course of the preparation.
Of the above compounds, magnesium compounds having no reducing ability (a-2) are preferable, and of these, halogen-containing magnesium compounds are particularly preferable. Above all, magnesium chloride, alkoxymagnesium chloride or aryloxymagnesium chloride is preferably employed.
When the magnesium compound is solid, it can be changed to liquid by the use of an electron donor (d-1) in the invention. Examples of the electron donors (d-1) employable herein include alcohols, carboxylic acids, aldehydes, amines and metallic acid esters.
Examples of the alcohols include aliphatic alcohols, such as methanol, ethanol, propanol, isopropyl alcohol, butanol, pentanol, hexanol, 2-methylpentanol, 2-ethylbutanol, heptanol, 2-ethylhexanol, octanol, decanol, dodecanol, tetradecyl alcohol, octadecyl alcohol, undecenol, oleyl alcohol, stearyl alchol and ethylene glycol; alicyclic alcohols, such as cyclohexanol and methylcyclohexanol; aromatic alcohols, such as benzyl alcohol, methylbenzyl alcohol, isopropylbenzyl alcohol, xcex1-methylbenzyl alcohol, xcex1,xcex1-dimethylbenzyl alcohol, phenylethyl alcohol, cumyl alcohol, phenol, cresol, xylenol, ethylphenol, propylphenol, nonylphenol and naphthol; alkoxy group-containing alcohols, such as n-butyl cellosolve, ethyl cellosolve and 1-butoxy-2-propanol; and halogen-containing alcohols, such as trichloromethanol, trichloroethanol and trichlorohexanol.
Examples of the carboxylic acids preferably used include those of 7 or more carbon atoms, such as caprylic acid, 2-ethylhexanoic acid, nonylic acid and undecylenic acid.
Examples of the aldehydes preferably used include those of 7 or more carbon atoms, such as caprylaldehyde, 2-ethylhexylaldehyde, undecylaldehyde, benzaldehyde, tolualdehyde and naphthaldehyde.
Examples of the amines preferably used include those of 6 or more carbon atoms, such as heptylamine, octylamine, 2-ethylhexylamine, nonylamine, decylamine, undecylamine and laurylamine.
Examples of the metallic acid esters include tetraethoxytitanium, tetra-n-propoxytitanium, tetra-i-propoxytitanium, tetrabutoxytitanium, tetrahexoxytitanium, tetrabutoxyzirconium and tetraethoxyzirconium. In the metallic acid esters, silicic acid esters described later as the organosilicon compounds having no active hydrogen (c-1) are not included.
These electron donors (d-1) may be used in combination of two or more kinds, and may be used in combination with the later-described electron donor (d) other than those described above. Of these, alcohols and metallic acid esters are preferably employed, and alcohols of 6 or more carbon atoms are particularly preferably employed.
When the magnesium compound is changed to liquid by the use of the electron donor (d-1), the electron donor of 6 or more carbon atoms as the electron donor (d-1) is used in an amount of usually not less than about 1 mol, preferably 1 to 40 mol, more preferably 1.5 to 12 mol, based on 1 mol of the magnesium compound. The electron donor of 5 or less carbon atoms as the electron donor (d-1) is used in an amount of usually not less than about 15 mol based on 1 mol of the magnesium compound.
In the contact of the solid magnesium compound with the electron donor (d-1), a hydrocarbon solvent can be employed. Examples of the hydrocarbon solvents include aliphatic hydrocarbons, such as pentane, hexane, heptane, octane, decane, dodecane, tetradecane and kerosine; alicyclic hydrocarbons, such as cyclopentane, methylcyclopentane, cyclohexane, methylcyclohexane, cyclooctane and cyclohexene; aromatic hydrocarbons, such as benzene, toluene, xylene, ethylbenzene, cumene and cymene; and halogenated hydrocarbons, such as carbon tetrachloride, dichloroethane, dichloropropane, trichloroethylene and chlorobenzene.
When an aromatic hydrocarbon is used as the hydrocarbon solvent and an alcohol is used as the electron donor (d-1), the alcohol has only to be used in the amount previously described as the amount of the electron donor of 6 or more carbon atoms irrespective of the type (number of carbon atoms) of the alcohol, whereby the magnesium compound can be dissolved. When an aliphatic hydrocarbon and/or an alicyclic hydrocarbon is used, the alcohol as the electron donor (d-1) is used in the above-mentioned amount according to the number of carbon atoms.
In the present invention, it is preferable to use a liquid magnesium compound (a) prepared by contacting the solid magnesium compound with the electron donor (d-1) in the hydrocarbon solvent. In order to dissolve the solid magnesium compound in the electron donor (d-1), a process comprising contacting the solid magnesium compound with the electron donor (d-1) preferably in the presence of a hydrocarbon solvent and then heating the contact product when needed is generally used. This contact is carried out at a temperature of usually 0 to 300xc2x0 C., preferably 20 to 180xc2x0 C., more preferably 50 to 150xc2x0 C., for a period of about 15 minutes to 15 hours, preferably about 30 minutes to 10 hours.
(b) Liquid Titanium Compound
As the liquid titanium compound, a tetravalent titanium compound is particularly preferably employed. The tetravalent titanium compound is, for example, a compound represented by the following formula:
Ti(OR)gX4xe2x88x92g
wherein R is a hydrocarbon group, X is a halogen atom, and 0xe2x89xa6gxe2x89xa64.
Examples of such compounds include:
titanium tetrahalides, such as TiCl4, TiBr4 and Til4;
alkoxytitanium trihalides, such as Ti(OCH3)Cl3, Ti(OC2H5)Cl3, Ti(O-n-C4H9)Cl3, Ti(OC2H5)Br3 and Ti(O-iso-C4H9)Br3;
dialkoxytitanium dihalides, such as Ti(OCH3)2Cl2, Ti(OC2H5)2Cl2, Ti(O-n-C4H9)2Cl2 and Ti(OC2H5)2Br2;
trialkoxytitanium monohalides, such as Ti(OCH3)3Cl, Ti(OC2H5)3Cl, Ti(O-n-C4H9)3Cl and Ti(OC2H5)3Br; and
tetraalkoxytitaniums, such as Ti(OCH3)4, Ti(OC2H5)4, Ti(O-n-C4H9)4, Ti(O-iso-C4H9)4 and Ti(O-2-ethylhexyl)4.
Of these, titanium tetrahalides are preferable, and titanium tetrachloride is particularly preferable.
These titanium compounds may be used in combination of two or more kinds. The titanium compound may be used after diluted with such a hydrocarbon solvent as previously described for making the magnesium compound liquid.
(c) Organosilicon Compound or Organosilicon Aluminum Compound
In the preparation of the solid titanium catalyst component, an organosilicon compound (c-1) or an organosilicon aluminum compound (c-2) is employed.
(c-1) Organosilicon Compound
As the organosilicon compound (c-1), an organosilicon compound having no active hydrogen is preferably employed, and such a compound is, for example, a compound represented by the following formula:
R1xR2ySi(OR3)z
wherein R1 and R2 are each independently a hydrocarbon group or a halogen, and R3 is a hydrocarbon group.
Examples of the hydrocarbon groups indicated by R1, R2 and R3 include an alkyl group, a cycloalkyl group, an aryl group, an alkylaryl group, an arylalkyl group and an alkenyl group. These groups may be substituted with a halogen or an amino group.
x is a number of 0xe2x89xa6x less than 2, y is a number of 0xe2x89xa6y less than 2, and z is a number of 0 less than zxe2x89xa64.
Examples of the organosilicon compounds represented by the above formula include tetramethoxysilane, tetraethoxysilane, tetrepropoxysilane, tetrabutoxysilane, tetrakis(2-ethylhexyloxy)silane, ethyltrimethoxysilane, ethyltriethoxysilane, vinyltrimethoxysilane, methyltrimethoxysilane, n-propyltriethoxysilane, decyltrimethoxysilane, cyclopentyltrimethoxysilane, 2-mehylcyclopentyltrimethoxysilane, 2,3-dimethylcyclopentyltrimethoxysilane, cyclohexyltrimethoxysilane, 2-norbornanetrimethoxysilane, 2-norbornanemethyldimethoxysilane, phenyltrimethoxysilane, xcex3-chloropropyltrimethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, vinyltriethoxysilane, t-butyltriethoxysilane, n-butyltriethoxysilane, isobutyltriethoxysilane, decyltriethoxysilane, cyclopentyltriethoxysilane, cyclohexyltriethoxysilane, 2-norbornanetriethoxysilane, phenyltriethoxysilane, xcex3-aminopropyltriethoxysilane, chlorotriethoxysilane, ethyltriisopropoxysilane, vinyltributoxysilane, trimethylphenoxysilane, methyltriallyloxysilane, vinyltris(xcex2-methoxyethoxy)silane, vinyltriacetoxysilane, dimethyldimethoxysilane, diisopropyldimethoxysilane, t-butylmethyldimethoxysilane, dicyclopentyldimethoxysilane, bis(2-methylcyclopentyl)dimethoxysilane, bis(2,3-dimethylcyclopentyl)dimethoxysilane, dicyclohexyldimethoxysilane, cyclohexylmethyldimethoxysilane, diphenyldimethoxysilane, phenylmethyldimethoxysilane, bis-o-tolyldimethoxysilane, bis-m-tolyldimethoxysilane, bis-p-tolyldimethoxysilane, bis(ethylphenyl)dimethoxysilane, dimethyldiethoxysilane, t-butylmethyldiethoxysilane, t-amylmethyldiethoxysilane, dicyclopentyldiethoxysilane, diphenyldiethoxysilane, bis-p-tolyldiethoxysilane, cyclohexylmethyldiethoxysilane, trimethylmethoxysilane, trimethylethoxysilane, tricyclopentylmethoxysilane, tricylopentylethoxysilane, dicyclopentylmethylmethoxysilane, dicylopentylethylmethoxysilane, hexenyltrimethoxysilane, cyclopentyldimethylmethoxysilane, cyclopentyldiethylmethoxysilane, dicyclopentylmethylethoxysilane and cyclopentyldimethylethoxysilane.
In addition to the organosilicon compounds represented by the above formula, dimethyltetraethoxydisiloxane is also employable as the organosilicon compound (c-1).
Of the above compounds, tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane and cyclohexylmethyldimethoxysilane are preferably used, and from the viewpoint of catalytic activity, tetraethoxysilane is particularly preferably used.
In the present invention, the organosilicon compound (c-1) having no active hydrogen is not necessarily used as such in the preparation of the solid titanium catalyst component, and other compounds capable of producing an organosilicon compound having no active hydrogen during the course of the preparation of the solid titanium catalyst component are also employable.
(c-2) Organosilicon Aluminum Compound
As the organosilicon aluminum compound (c-2), any of an organic compound containing both a silicon and an organic compound containing aluminum is employable. In the present invention, however, an aluminosiloxane compound is preferably used.
The aluminosiloxane compound is, for example, a compound represented by the following formula:
[Al(OR4)2(OSiR53)]m,
[Al(OR6) (OSiR73)2]p, or
[Al(OSiR83)3]2.
In the above formulas, R4 to R8 are each independently an alkyl group of 1 to 12 carbon atoms or an aryl group of 6 to 12 carbon atoms, and m and p are each an integer of 2 or greater. In the above formulas, R4 and R6 are each preferably at least one group selected from the group consisting of ethyl, propyl, isopropyl and t-butyl. R5, R7 and R8 are each preferably at least one group selected from the group consisting of methyl, ethyl, propyl, isopropyl, t-butyl and phenyl.
In the present invention, an aluminosiloxane compound having an Al:Si molar ratio of 1:1, 1:2 or 1:3 is preferably used as the organosilicon aluminum compound (c-2).
The compound represented by the formula [Al(OR4)2(OSiR53)]m has an Al:Si molar ratio of 1:1, and examples of such compounds include those represented by the following formulas. In this specification, a methyl group and an isopropyl group are sometimes represented by xe2x80x9cMexe2x80x9d and xe2x80x9ciPrxe2x80x9d, respectively. 
The compound represented by the formula [Al(OR6) (OSiR73)2]p has an Al:Si molar ratio of 1:2, and examples of such compounds include those represented by the following formulas. 
The compound represented by the formula [Al(OSiR83)3]2 has an Al:Si molar ratio of 1:3, and examples of such compounds include those represented by the following formula. 
The aluminosiloxane compound may be prepared by any process, and can be prepared by, for example, the method described in, for example, K. Forting, W. E. Streib, K. G. Caulton, O. Poncelet and L. G. Hubert-Pfalzgret, Polyhedron, 10(14), 1639-1646 (1991). The structure of the aluminosiloxane compound thus prepared can be identified by IR and 1H-NMR.
For example, the aluminosiloxane of the formula [Al(OiPr)2(OSiMe3)]m employable in the invention has the following spectral information.
IR (cmxe2x88x921): 1250 (Sixe2x80x94C); xe2x88x921180, 1130 (Cxe2x80x94CH3); 1170; 950 (Sixe2x80x94O); 760; 640 (Alxe2x80x94OR)
1H-NMR (CDCl3, 0.1M, 25xc2x0 C.) (ppm): 4.47-4.08 (m, OCHMe2, 2H); 1.42; 1.27; 1.47; 1.36; 1.21; 1.10; 1.06 (d, J=6 Hz, OCHMe2, 12H); 0.25, 0.22, 0.21 (s, OSiMe2, 9H)
(d) Another Electron Donor
The solid titanium catalyst component for use in the invention may contain another electron donor (d) if necessary, in addition to the liquid magnesium compound (a), the liquid titanium compound (b) and the organosilicon compound or the organosilicon aluminum compound (c).
Examples of the electron donors (d) include organic acid esters, organic acid halides, organic acid anhydrides, ethers, ketones, tertiary amines, phosphorous acid esters, phosphoric acid esters, carboxylic acid amides, nitriles, aliphatic carbonates and pyridines.
More specifically, there can be mentioned:
organic acid esters of 2 to 18 carbon atoms, such as methyl formate, methyl acetate, ethyl acetate, vinyl acetate, propyl acetate, i-butyl acetate, t-butyl acetate, octyl acetate, cyclohexyl acetate, methyl chloroacetate, ethyl dichloroacetate, ethyl propionate, ethyl pyruvate, ethyl pivalate, methyl butyrate, ethyl valerate, methyl methacrylate, ethyl crotonate, ethyl cyclohexanecarboxylate, methyl benzoate, ethyl benzoate, propyl benzoate, butyl benzoate, octyl benzoate, cyclohexyl benzoate, phenyl benzoate, benzyl benzoate, methyl toluylate, ethyl toluylate, amyl toluylate, ethyl ethylbenzoate, methyl anisate, ethyl anisate and ethyl ethoxybenzoate;
acid halides of 2 to 15 carbon atoms, such as acetyl chloride, benzoyl chloride and toluyl chloride;
acid anhydrides, such as acetic anhydride, phthalic anhydride, maleic anhydride, benzoic anhydride, trimellitic anhydride and tetrahydrophthalic anhydride;
ethers of 2 to 20 carbon atoms, such as methyl ether, ethyl ether, isopropyl ether, butyl ether, amyl ether, tetrahydrofuran, ethyl benzyl ether, ethylene glycol dibutyl ether, anisole and diphenyl ether;
ketones of 3 to 20 carbon atoms, such as acetone, methyl ethyl ketone, methyl isobutyl ketone, ethyl-n-butyl ketone, acetophenone, benzophenone, benzoquinone and cyclohexanone;
tertiary amines, such as trimethylamine, triethylamine, tributylamine, tribenzylamine and tetramethylethylenediamine;
phosphorous acid esters, such as trimethyl phosphite, triethyl phosphite, tri-n-propyl phosphite, triisopropyl phosphite, tri-n-butyl phosphite, triisobutyl phosphite, diethyl-n-butyl phosphite and diethylphenyl phosphite;
phosphoric acid esters, such as trimethyl phosphate, triphenyl phosphate and tritolyl phosphate;
acid amides, such as N,N-dimethylacetamide, N,N-diethylbenzamide and N,N-dimethyltoluamide;
nitriles, such as acetonitrile, benzonitrile and tolunitrile;
aliphatic carbonates, such as dimethyl carbonate, diethyl carbonate and ethylene carbonate; and
pyridines, such as pyridine, methylpyridine, ethylpyridine and dimethylpyridine.
These compounds can be used in combination of two or more kinds.
The solid titanium catalyst component (A) for use in the invention can be prepared from the above components by, for example, the following process (1) or (2).
(1) The liquid magnesium compound (a) is contacted with the liquid titanium compound (b) in the presence of the organosilicon compound or the organosilicon aluminum compound (c) (sometimes referred to as xe2x80x9corganosilicon compound (c)xe2x80x9d simply hereinafter) in an amount of 0.25 to 0.35 mol based on 1 mol of the magnesium compound (a), and the resulting contact product is heated to a temperature of 90 to 115xc2x0 C. and maintained at this temperature.
(2) The contact product prepared in the same manner as in the process (1) is maintained at a temperature of 90 to 115xc2x0 C., and in this course, the organosilicon compound (c) is further added in an amount of not more than 0.5 mol based on 1 mol of the magnesium compound (a) between the time of a temperature lower by 10xc2x0 C. than the temperature maintained and the time of completion of the temperature rise, or after completion of the temperature rise, and contacted with the contact product.
Of the above processes, the process (1) is preferably used in the preparation of the solid titanium catalyst component (A) from the viewpoint of catalytic activity of the resulting solid titanium catalyst component.
For contacting the components in the above processes, the organosilicon compound (c) is desirably used in the amount specified as above based on the liquid magnesium compound (a). The liquid titanium compound (b) is desirably used in such a sufficient amount that a solid can be precipitated by the contact even if any special precipitating means is not used. Although the amount of the liquid titanium compound (b) used varies depending upon the type thereof, contact conditions, amount of the organosilicon compound (c), etc., it is usually not less than about 1 mol, preferably about 5 to about 200 mol, particularly preferably about 10 to about 100 mol, based on 1 mol of the liquid magnesium compound (a). The titanium compound (b) is used in an amount of preferably more than 1 mol, particularly preferably not less than 5 mol, based on 1 mol of the organosilicon compound (c).
The process for preparing the solid titanium catalyst component (A) is described below in more detail.
The liquid magnesium compound (a) and/or the titanium compound (b) used for preparing the solid titanium catalyst component (A) may contain the organosilicon compound (c). In this case, it is unnecessary to newly add the organosilicon compound (c) in the contact of the magnesium compound (a) with the titanium compound (b), however, the organosilicon compound (c) may be added if in either case the whole amount of the organosilicon compound (c) based on the magnesium compound (a) is in the above range.
The liquid magnesium compound (a) containing the organosilicon compound (c) is obtained by, for example, contacting the organosilicon compound (c) with the liquid magnesium compound (a) for a given period of time. The contact time (t) is as follows. When the contact temperature (Temp) is not higher than 55xc2x0 C., the contact time is a time satisfying the condition of t greater than (3-(Temp-50)/5) hour(s), preferably t greater than (4-(Temp-50)/5) hour(s). When the contact temperature exceeds 55xc2x0 C., the contact time is at least 1 hour, preferably not less than 2 hours. The contact temperature is in the range of usually 20 to 100xc2x0 C., preferably higher than 55xc2x0 C. and not higher than 90xc2x0 C.
In the process (1) for preparing the solid titanium catalyst component (A), the contact of the liquid magnesium compound (a) with the liquid titanium compound (b) is carried out in the presence of the organosilicon compound (c) at a low temperature at which a solid is not produced rapidly, and is desirably carried out at a temperature of specifically xe2x88x9270 to +50xc2x0 C., preferably xe2x88x9250 to +30xc2x0 C., more preferably xe2x88x9240 to +20xc2x0 C. The temperatures of the solutions used for the contact may be different from each other. If the contact temperature at the beginning of the contact is too low to precipitate a solid in the contact product, low-temperature contact may be conducted for a long period of time to precipitate a solid.
In the process (1), the contact product obtained above is then slowly heated to a temperature of 90 to 115xc2x0 C. to slowly precipitate a solid and maintained at this temperature. The period of time for maintaining the temperature is in the range of usually 0.5 to 6 hours, preferably about 1 to 4 hours. The period of time necessary for the temperature rise greatly varies depending upon the scale of the reactor, etc.
By the contact of the liquid magnesium compound (a) with the liquid titanium compound (b) in the presence of the organosilicon compound (c) under the above conditions, a granular or spherical solid titanium catalyst component having an excellent particle size distribution can be obtained. When ethylene is subjected to slurry polymerization using such a solid titanium catalyst component of excellent particle morphology, a granular or spherical ethylene polymer having an excellent particle size distribution, high bulk density and excellent fluidity can be obtained.
In the process (2) for preparing the solid titanium catalyst component (A), the contact product is heated to a temperature of 90 to 115xc2x0 C. and maintained at this temperature for usually 0.5 to 6 hours, preferably 1 to 4 hours, similarly to the process (1). In this course, however, the organosilicon compound (c) in an amount of not more than 0.5 mol based on 1 mol of the magnesium compound (a) is further added to the contact product between the time when a temperature is lower by 10xc2x0 C. than the temperature maintained and the time when the temperature rise is completed, or after the temperature rise is completed (preferably immediately after the temperature rise).
The solid titanium catalyst component (A) prepared as above contains magnesium, titanium, a halogen and the organosilicon compound (c). In the solid titanium catalyst component (A), the magnesium/titanium atomic ratio is in the range of about 2 to about 100, preferably about 4 to about 50, more preferably about 5 to about 30, and when the organosilicon compound (c-1) is used, the magnesium/titanium molar ratio is in the range of 3.0 to 4.0, preferably 3.1 to 3.8, more preferably 3.2 to 3.7. The titanium atom is desirably contained in an amount of not less than 7.8% by weight, preferably not less than 8.0% by weight. The halogen/titanium atomic ratio is desired to be in the range of about 4 to about 100, preferably about 5 to about 90, more preferably about 8 to about 50, and the organosilicon compound (c)/titanium molar ratio is desired to be in the range of about 0.01 to about 100, preferably about 0.1 to about 10, more preferably about 0.2 to about 6.
The organosilicon compound (c)/magnesium molar ratio is desired to be in the range of about 0.001 to about 0.1, preferably about 0.002 to about 0.08, particularly preferably 0.005 to 0.05.
The solid titanium catalyst component (A) for use in the invention may further contain other additives, such as a carrier, in addition to the above components. When the carrier is used, the carrier may be contained in an amount of not more than 500% by weight, preferably not more than 400% by weight, more preferably not more than 300% by weight, still more preferably not more than 200% by weight, based on the catalyst component. The composition of the solid titanium catalyst component can be measured by ICP (Inductively Coupled Plasma-Atomic Emission Spectroscopy), gas chromatography or the like, after the solid titanium catalyst component is sufficiently washed with a large amount of hexane and dried under the conditions of 0.1 to 1 Torr and room temperature for not less than 2 hours.
The shape of the solid titanium catalyst component (A) for use in the invention is desired to be granular or almost spherical, and the specific surface area thereof is not less than about 10 m2/g, preferably about 30 to 500 m2/g. In the present invention, the solid titanium catalyst component is usually used after washed with a hydrocarbon solvent.
In the present invention, an ethylene polymerization catalyst containing the above-described solid titanium catalyst component (A) is employed.
As the ethylene polymerization catalyst for use in the invention, a catalyst formed from the solid titanium catalyst component (A) and an organometallic compound (B) is preferably employed. The organometallic compound capable of forming the ethylene polymerization catalyst for use in the invention is preferably one containing a metal selected from Group 1, Group 2 and Group 13 of the periodic table, and examples of such compounds include an organoaluminum compound, an alkyl complex salt of a Group 1 metal and aluminum, and an organometallic compound of a Group 2 metal.
The organoaluminum compound is, for example, an organoaluminum compound represented by the following formula:
RanAlX3xe2x88x92n
wherein Ra is a hydrocarbon group of 1 to 12 carbon atoms, X is a halogen or hydrogen, and n is 1 to 3.
In the above formula, Ra is a hydrocarbon group of 1 to 12 carbon atoms, such as an alkyl group, a cycloalkyl group or an aryl group. Examples of such groups include methyl, ethyl, n-propyl, isopropyl, isobutyl, pentyl, hexyl, octyl, cyclopentyl, cyclohexyl, phenyl and tolyl.
Examples of such organoaluminum compounds include:
trialkylaluminums, such as trimethylaluminum,
triethylaluminum, triisopropylaluminum,
triisobutylaluminum, trioctylaluminum and tri-2-ethylhexylaluminum;
alkenylaluminums, such as isoprenylaluminum;
dialkylaluminum halides, such as dimethylaluminum chloride, diethylaluminum chloride, diisopropylaluminum chloride, diisobutylaluminum chloride and dimethylaluminum bromide;
alkylaluminum sesquihalides, such as methylaluminum sesquichloride, ethylaluminum sesquichloride, isopropylaluminum sesquichloride, butylaluminum sesquichloride and ethylaluminum sesquibromide;
alkylaluminum dihalides, such as methylaluminum dichloride, ethylaluminum dichloride, isopropylaluminum dichloride and ethylaluminum dibromide; and
alkylaluminum hydrides, such as diethylaluminum hydride and diisobutylaluminum hydride.
Also employable as the organoaluminum compound is a compound represented by the following formula.
RanAlY3xe2x88x92n
In the above formula, Ra is the same as above, Y is xe2x80x94ORb group, xe2x80x94OSiRc3 group, xe2x80x94OAlRd2 group, xe2x80x94NRe2 group, xe2x80x94SiRf3 group or xe2x80x94N(Rg)AlRh2 group, and n is 1 to 2. Rb, Rc, Rd and Rh are each independently a hydrocarbon group, such as methyl, ethyl, isopropyl, isobutyl, cyclohexyl or phenyl, Re is hydrogen, methyl, ethyl, isopropyl, phenyl, trimethylsilyl or the like, and Rf and Rg are each methyl, ethyl or the like.
Examples of such organoaluminum compounds include the following compounds:
(1) compounds represented by RanAl(ORb)3xe2x88x92n, such as dimethylaluminum methoxide, diethylaluminum ethoxide and diisobutylaluminum methoxide;
(2) compounds represented by RanAl (OSiRc3)3xe2x88x92n, such as Et2Al (OSiMe3), (iso-Bu)2Al(OSiMe3) and (iso-Bu)2Al (OSiEt3);
(3) compounds represented by RanAl(OAlRd2)3xe2x88x92n, such as Et2AlOAlEt2 and (iso-Bu)2AlOAl(iso-Bu)2;
(4) compounds represented by RanAl(NRe2)3xe2x88x92n, such as Me2AlNEt2, Et2AlNHMe, Me2AlNHEt, Et2AlN(Me3Si)2 and (iso-Bu)2AlN(Me3Si)2;
(5) compounds represented by RanAl(SiRf3)3xe2x88x92n, such as (iso-Bu)2AlSiMe3; and
(6) compounds represented by RanAl[N(Rg)xe2x80x94AlRh2]3xe2x88x92n, such as Et2AlN(Me)xe2x80x94AlEt2 and (iso-Bu)2AlN(Et)Al(iso-Bu)2.
Also available are compounds analogous to the above compounds, such as organoaluminum compounds wherein two or more aluminum atoms are bonded through an oxygen atom or a nitrogen atom. Examples of such compounds include (C2H5)2AlOAl(C2H5)2, (C4H9)2AlOAl(C4H9)2 and (C2H5)2AlN(C2H5)Al(C2H5)2. Aluminoxanes, such as methylaluminoxane, are also available.
The alkyl complex salt of a Group 1 metal and aluminum is, for example, a compound represented by the following formula:
M1AlRj4
wherein M1 is Li, Na or K, and Rj is a hydrocarbon group of 1 to 15 carbon atoms.
Examples of such compounds include LiAl(C2H5)4 and LiAl(C7H15)4.
The organometallic compound of a Group 2 metal is, for example, a compound represented by the following formula:
RkRlM2
wherein Rk and Rl are each a hydrocarbon group of 1 to 15 carbon atoms or a halogen, they may be the same or different except that each of them is a halogen, and M2 is Mg, Zn or Cd.
Examples of such compounds include diethylzinc, diethylmagnesium, butylethylmagnesium, ethylmagnesium chloride and butylmagnesium chloride.
Of the organometallic compounds mentioned above, compounds represented by Ra3AlX3xe2x88x92n, RanAl(ORb)3xe2x88x92n and RanAl(OAlRd2)3xe2x88x92n, particularly trialkylaluminums, are preferably employed. These compounds can be used in combination of two or more kinds.
Onto the ethylene polymerization catalyst for use in the invention, olefins may be prepolymerized. The ethylene polymerization catalyst for use in the invention may further contain other components useful for ethylene polymerization in addition to the above components.
The ethylene polymerization catalyst for use in the invention exhibits extremely high activity in the polymerization or copolymerization of ethylene.
In the present invention, using the catalyst containing the solid titanium catalyst component (A), ethylene is polymerized singly or ethylene and another xcex1-olefin are copolymerized to prepare an ethylene polymer composition. The polymerization can be carried out by any of batchwise, semi-continuous and continuous processes. It is preferable to polymerize ethylene singly or copolymerize ethylene and another xcex1-olefin in plural steps including the following steps (I) and (II) to prepare an ethylene polymer composition.
The olefin other than ethylene that is used in the copolymerization of ethylene and another xcex1-olefin is, for example, an xcex1-olefin of 3 to 20 carbon atoms. Examples of such xcex1-olefins include straight-chain or branched xcex1-olefins, such as propylene, 1-butene, 1-pentene, 1-hexene, 3-methyl-1-butene, 3-methyl-1-pentene, 3-ethyl-1-pentene, 4-methyl-1-pentene, 4,4-dimethyl-1-pentene, 4-methyl-1-hexene, 4,4-dimethyl-1-hexene, 4-ethyl-1-hexene, 3-ethyl-1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene and 1-eicosene. These xcex1-olefins may be used singly or in combination of two or more kinds.
In the polymerization in the present invention, small amounts of other unsaturated compounds, such as vinyl compounds, cycloolefins and polyene compounds, can be copolymerized. For example, there can be copolymerized aromatic vinyl compounds, such as styrene, substituted styrenes, allylbenzene, substituted allylbenzenes, vinylnaphthalenes, substituted vinylnaphthalenes, allylnaphthalenes and substituted allylnaphathalenes; alicyclic vinyl compounds, such as vinylcyclopentane, substituted vinylcyclopentanes, vinylcyclohexane, substituted vinylcyclohexanes, vinylcycloheptane, substituted vinylcycloheptanes and allylnorbornane; cycloolefins, such as cyclopentene, cycloheptene, norbornene, 5-methyl-2-norbornene, tetracyclododecene and 2-methyl-1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene; and silane unsaturated compounds, such as allyltrimethylsilane, allyltriethylsilane, 4-trimethylsilyl-1-butene, 6-trimethylsilyl-1-hexene, 8-trimethylsilyl-1-octene and 10-trimethylsilyl-1-decene.
The step (I) is a step to homopolymerize ethylene or copolymerize ethylene and another xcex1-olefin using the catalyst containing the solid titanium catalyst component (A), and is
a step to prepare an ethylene polymer (i) having an xcex1-olefin content of not more than 30% by weight, preferably 0 to 20% by weight, more preferably 0 to 10% by weight, and an intrinsic viscosity [xcex7] of at least 1.5 times, preferably not less than 2 times, more preferably 3 to 20 times, the intrinsic viscosity of an ethylene polymer (ii) obtained in the later-described step (II), and ranging from 1 to 12 dl/g, preferably from 1.5 to 12 dl/g, more preferably from 2 to 10 dl/g.
When the ethylene copolymer composition is applied to film use, the intrinsic viscosity [xcex7] of the ethylene polymer (i) is desired to be in the range of 5 to 20 times, preferably 7 to 15 times, the intrinsic viscosity [xcex7] of the ethylene polymer (ii). The intrintrinsic viscosity [xcex7] used herein is measured in decalin at 135xc2x0 C., an is expressed by dl/g.
The upper limit of the intrinsic viscosity [xcex7] of the ethylene polymer (i) is not specifically restricted as long as the intrinsic viscosity [xcex7] of the ethylene polymer (i) is at least 1.5 times the intrinsic viscosity [xcex7] of the ethylene polymer (ii) and the polymerization is feasible, but the upper limit is desired to be usually not more than 50 times.
The step (II) is a step to homopolymerize ethylene or copolymerize ethylene and another xcex1-olefin, and is
a step to prepare an ethylene polymer (ii) having an xcex1-olefin content of not more than 15% by weight, preferably 0 to 10% by weight, more preferably 0 to 5% by weight, and an intrinsic viscosity [xcex7] of 0.3 to 3 dl/g, preferably 0.4 to 2.5 dl/g, preferably from 0.5 to 2 dl/g.
When the xcex1-olefin content of the ethylene polymer (ii) is in the above range, a composition having excellent resistance to environmental stress crack is obtained, so that the above range is preferable. When the intrinsic viscosity [xcex7] of the ethylene polymer (II) is in the above range, a composition having excellent processability, impact strength and tensile strength is obtained, and a molded article having little surface roughening can be produced, so that the above range is preferable.
In the present invention, the step (II) is carried out in the presence of the ethylene polymer (i) obtained in the step (I), or the step (I) is carried out in the presence of the ethylene polymer (ii) obtained in the step (II). In this process, in the step (latter step) that is carried out in the presence of the ethylene polymer obtained in the former step, the aforesaid ethylene polymerization catalyst may be newly added, but it is preferable to continuously use the ethylene polymerization catalyst used in the former step. When the ethylene polymerization catalyst used in the former step is continuously used, the amount of the catalyst can be decreased, and a composition having less fish-eye can be obtained, so that such use is preferable.
In the present invention, an ethylene polymer is produced in the latter step in the presence of the ethylene polymer obtained in the former step, whereby an ethylene polymer composition is prepared. The intrinsic viscosity [xcex7]B of the ethylene polymer produced in the latter step can be determined by the following formula:
[xcex7]C=WA[xcex7]A+WB[xcex7]B
wherein [xcex7]A is an intrinsic viscosity of the ethylene polymer obtained in the former step, [xcex7]B is an intrinsic viscosity obtained in the latter step, [xcex7]C is an intrinsic viscosity of the ethylene polymer composition, WA is a weight ratio of the ethylene polymer obtained in the former step to the ethylene polymer composition, WB is a weight ratio of the ethylene polymer obtained in the latter step to the ethylene polymer composition, and WA+WB=1.
Although the polymerization in the step (I) and the step (II) may be any of slurry polymerization and gas phase polymerization, the slurry polymerization is preferable. The polymerization in the step (I) and the step (II) may be carried out in the presence of an inert solvent. Examples of the inert solvents employable in the polymerization include aliphatic hydrocarbons, such as butane, pentane, hexane, heptane, octane, decane, dodecane and kerosine; alicyclic hydrocarbons, such as cyclopentane, methylcyclopentane, cyclohexane and methylcyclohexane; aromatic hydrocarbons, such as benzene, toluene, xylene and ethylbenzene; and halogenated hydrocarbons, such as ethylene chloride and chlorobenzene.
In the step (I) and the step (II) in the invention, the ethylene polymerization catalyst is desirably used in an amount of usually 0.0001 to 0.1 mmol, preferably 0.001 to 0.05 mmol, in terms of Ti atom, based on 1 liter of the polymerization volume.
Although the polymerization conditions in the step (I) and the step (II) are not specifically restricted, these steps are desirably carried out under the conditions of a temperature of usually about 20 to 120xc2x0 C., preferably 50 to 100xc2x0 C., and a pressure of atmospheric pressure to 9.8 MPa (atmospheric pressure to 100 kg/cm2), preferably about 0.2 to 4.9 MPa (about 2 to 50 kg/cm2). When the organometallic compound (B) is used in combination, this compound (B) is used in such an amount that the amount of the metal atom in the organometallic compound (B) becomes usually 1 to 2000 mol based on 1 mol of the titanium atom in the solid titanium catalyst component (A).
In the step (I) and the step (II), the polymerization can be carried out in the presence of hydrogen to control the molecular weight of the resulting polymer.
The ethylene polymer composition obtained in the invention contains the ethylene polymer (i) obtained in the step (I) and the ethylene polymer (ii) obtained in the step (II).
In the present invention, the step (I) and the step (II) are desirably carried out in such a manner that the amount of the ethylene polymer (i) obtained in the step (I) becomes 40 to 70 parts by weight, preferably 45 to 60 parts by weight, and the amount of the ethylene polymer (ii) obtained in the step (II) becomes 60 to 30 parts by weight, preferably 55 to 40 parts by weight, each amount being based on 100 parts by weight of the resulting whole ethylene polymer composition.
By the process for preparing an ethylene polymer composition having the step (I) and the step (II) according to the invention, an ethylene polymer composition having an intrinsic viscosity [xcex7] of 1 to 6 dl/g, preferably 1.5 to 5 dl/g, and a density of not less than 0.94 g/cm3, preferably 0.94 to 0.97 g/cm3, more preferably 0.95 to 0.97 g/cm3, is obtained.
The xcex1-olefin content in the ethylene polymer composition obtained by the invention is desired to be not more than 20% by weight, preferably 0 to 10% by weight. The molecular weight distribution (Mw/Mn) of the ethylene polymer composition obtained by the invention is relatively wide owing to the multi-step polymerization and is desired to be in the range of usually 20 to 45, preferably about 25 to 40.
The process for preparing an ethylene polymer composition according to the invention may further has, in addition to the step (I) and the step (II), a drying step for drying the resulting ethylene polymer composition at a temperature of about 50 to 110xc2x0 C., preferably about 70 to 110xc2x0 C. The ethylene polymer composition obtained by the invention has a high sintering temperature, and even if the composition is subjected to drying accompanied by heating, surface tackiness hardly occurs. Moreover, local overheating hardly takes place owing to the excellent particle size distribution. Hence, drying of the ethylene polymer composition can be efficiently carried out.
If the homopolymerization of ethylene or copolymerization of ethylene and another xcex1-olefin using a catalyst containing the solid titanium catalyst component (A) is carried out in one step without dividing it into two steps, the resulting polymer has a bulk specific gravity of usually 0.30 to 0.45 g/ml, preferably 0.33 to 0.45 g/ml.
The melt flow rate (in accordance with ASTM D 1238E, 190xc2x0 C.) of the ethylene polymer obtained in the one-step polymerization is desired to be in the range of 0.01 to 5000 g/10 min.
In the process for preparing an ethylene polymer composition according to the invention, an ethylene polymer composition can be prepared with extremely high polymerization activity, and obtainable is an ethylene polymer composition having excellent particle morphology. On this account, the ethylene polymer composition has a low catalyst content per unit of the polymer composition, and mold rusting hardly occurs in the molding process. In addition, the ethylene polymer composition obtained by the invention has a narrow particle size distribution and a relatively wide molecular weight distribution, and hence the composition has excellent moldability and scarcely has tackiness even under such high-temperature conditions as in the molding process.
Particles of Ethylene Polymer Composition
The particles of ethylene polymer composition according to the invention comprise an ethylene polymer composition obtained by homopolymerizing ethylene or copolymerizing ethylene and another xcex1-olefin and having a melt flow rate, as measured at 190xc2x0 C. in accordance with ASTM D 1238E, of 0.0001 to 0.5 g/10 min, preferably 0.0005 to 0.3 g/10 min, and a molecular weight distribution (Mw/Mn) of 20 to 45, preferably 25 to 40. The ethylene polymer composition desirably has an intrinsic viscosity [xcex7] of 1 to 6 dl/g, preferably 1.5 to 5 dl/g, a density of not less than 0.94 g/cm3, preferably 0.94 to 0.97 g/cm3, more preferably about 0.95 to 0.97 g/cm3, and an xcex1-olefin content of not more than 20% by weight, preferably 0 to 10% by weight.
The particles of ethylene polymer composition of the invention have:
a particle size distribution index, as determined by the following formula, of 1.1 to 2.0, preferably 1.1 to 1.8, more preferably 1.1 to 1.6,
Particle size distribution index={square root over (Polymer D84/Polymer D16)}
wherein Polymer D16 is a particle diameter obtained when 16% by weight of the whole particles of ethylene polymer composition can be sieved, and Polymer D84 is a particle diameter obtained when 84% by weight of the whole particles of ethylene polymer composition can be sieved,
a bulk density of 0.30 to 0.45 g/ml, preferably 0.32 to 0.45 g/ml, and
a fluidity index of 45 to 90, preferably 50 to 90.
The molecular weight distribution (Mw/Mn) of the ethylene polymer composition can be determined by measuring molecular weights by GPC (gel permeation chromatography) under the conditions of columns of Tosoh GMHHR-H(S)-HT 30 cmxc3x972 and GMH-HTL 30 cmxc3x972, a solvent of orthodichlorobenzene, a flow rate of 1.0 ml/min and a temperature of 140xc2x0 C.
The particle size distribution index of the particles of ethylene polymer composition can be determined in accordance with the above formula using a particle size distribution obtained by sieve analysis. The bulk density can be determined by JIS K 6721, and the fluidity index can be determined by measuring compressibility (%), angle of repose (degrees), angle of spatula (degrees) and uniformity coefficient in accordance with the method of Carr (Chemical Engineering, Jan. 18, 1965).
The particles of ethylene polymer composition of the invention can be preferably prepared by the aforesaid process for preparing an ethylene polymer composition according to the invention, and can be more preferably prepared by carrying out the polymerization of the step (I) and the step (II) as slurry polymerization in the aforesaid process for preparing an ethylene polymer composition according to the invention.
The particles of ethylene polymer composition of the invention comprise an ethylene polymer composition having a specific MFR and a relatively wide molecular weight distribution and have a narrow particle size distribution, a specific bulk density and a specific fluidity index, as described above.
Accordingly, the particles of ethylene polymer composition have a high sintering temperature, scarcely have tackiness even at such a high temperature as in the drying process and are almost free from adhesion to one another, so that they can be easily handled in various processes such as transportation, storage and introduction into a molding machine. Further, the particles of ethylene polymer composition scarcely contain a fine powder and have excellent particle morphology, so that they can be used as they are without pelletization. Moreover, the particles of ethylene polymer composition of the invention have excellent moldability. Hence, a molded article obtained by molding them exhibits excellent impact strength and tensile strength, has little surface roughening and hardly causes rusting of a mold.
As described above, the particles of ethylene polymer composition of the invention can industrially, extremely efficiently undergo subsequent processes, such as transportation, storage, introduction into a molding machine and molding, and the molded product obtained from the particles has excellent properties.
To the ethylene polymer composition and the particles of ethylene polymer composition obtained by the invention, additives, such as heat stabilizer, weathering stabilizer, antistatic agent, anti-blocking agent, lubricant, nucleating agent, pigment, dye and inorganic or organic filler, can be added when needed.
The ethylene polymer composition and the particles of ethylene polymer composition according to the invention have excellent moldability and can be molded by calendering, extrusion molding, injection molding, blow molding, press molding, stamping and the like.
In order to produce a sheet or a film from the ethylene polymer composition or the particles of ethylene polymer composition, for example, extrusion molding of the ethylene polymer composition (particles) is available. In the extrusion molding, hitherto known extrusion devices and molding conditions are adoptable. For example, using a single-screw extruder, a kneading extruder, a ram extruder or a gear extruder, a molten ethylene polymer composition is extruded from a T-die or the like to produce a sheet or a film (unstretched).
A stretched film is obtained by stretching the extruded sheet or film (unstretched) by, for example, tentering (lengthwise-widthwise stretching, widthwise-lengthwise stretching), simultaneous biaxial orientation or monoaxial stretching. Also an inflation film can be produced. The inflation film is produced by a process comprising melting the particles of ethylene polymer composition, extruding the molten resin through a circular slit die and inflating the extrudate with a prescribed air stream. The resin temperature in the extrusion of the molten particles of ethylene polymer composition is preferably in the range of 180 to 250xc2x0 C. The height of the frost line from the die surface is preferably in the range of 8 to 15 times the die diameter. The blow up ratio is preferably in the range of 1.5 to 6 times.
The film that is produced from the particles of ethylene polymer composition of the invention as described above desirably has a thickness of 5 to 60 xcexcm, preferably 6 to 50 xcexcm.
The film obtained as above has features of small gauge-variation and excellent tear strength.
In the present invention, the expression xe2x80x9csmall gauge-variationxe2x80x9d used herein means that a standard deviation value of film thickness at the space of 15 mm is not more than 1.5 xcexcm measured by continuous film-thickness measuring apparatuses K-306A and K-310C (products of Anritsu Co.), and the expression xe2x80x9cexcellent tear strengthxe2x80x9d used herein means that Elmendorf tear strength measured in accordance with JIS K7128 is not less than 70 N/cm in the MD direction and not less than 700 N/cm in the TD direction.
According to the invention, an ethylene polymer composition having a low content of fine powder, excellent particle morphology and excellent moldability, scarcely having tackiness even under such high-temperature conditions as in the drying or molding process and having excellent industrial-handling properties can be prepared with extremely high polymerization activity.
The particles of ethylene polymer composition of the invention scarcely have tackiness even when heated in the molding process or the like, are almost free from adhesion to one another and can be easily handled industrially. Further, the particles of ethylene polymer composition have excellent moldability and scarcely cause rusting of a mold. Moreover, the particles of ethylene polymer composition scarcely contain a fine powder, exhibit excellent particle morphology and can be molded as they are without pelletization. The molded article obtained by molding the particles of ethylene polymer composition of the invention has excellent impact strength and tensile strength and has little surface roughening. When the particles of ethylene polymer composition are applied to film use, the film has small gauge-variation and excellent tear strength.
The film of the invention is obtained from the particles of ethylene polymer composition and has small gauge-variation and excellent tear strength.